Ammonia recovery in soda ash production



J.. R. TAYLOR AMMONIA RECOVERY IN SODA 'ASH RODUCTION Filed Jun 17;1944- /nuen'rs J RJ12/7 I d@ fil-borne?.

May 24, 1949.

`column, say .80

Patented May 24, 1949 'AMMONIA .RECOVERY IN iSLODA-ASH PRODUCTION JohnRoss Taylor, Westmount, Quebec, Canada, assignor .to `Richard Kellogg'Wurtcle,odericlx Ontario, Canada Application J une 17, 1944, SerialfNo.,540,184

-in Canada Juney 24, 1943 l Claim. i1 This invention relates ,to kthevproduction of soda ash 'and .',Darticijilarly directed to -that portion"DI .the mdtlfiillnfd apparatus in which ammonia is 'recovered from ,thecarbonated liquor from which Asodium bicazbonate has been removed,

vwhich constitutes one stage :in the well known Production of soda'oshAmmonialis a relatively `expensive reagent in the production of ,sodaash. Its eihcient recovery is thus ,an important consideration. Instandard practice the ammoniastill or distiller is a tall f eet .h igh,consisting of a series oicast iron Qsectionsi'to feet in diameter. Heatis introducediatthebottomof the column. Scale formation :creates a,problem necessitating periodical .cleaningof the column. To reducesedimentation -and scale formation, sand traps are usually employed.tolclnove larger solid particles from theprelimed'liquor. Installationand operating costs arehigh.

The object ofthe present invention is to reiduce greatly theinstallation and operating costs of the ammonia recovery system. Moreparticularly the object-is to provide a :method and apparatus for therecovery of ammonia which is more economical in installation as lwell asoperating costs, and which substantially eliminates sedimentation fandscale vformation, thus permitting more continuity and-eiciency ofoperation.

lOther kobjects -will appear from the following descriptlonuwithreference L-to the accompanying dr-awingfinffwhich Figure 1 is aksideelevatinm, partly in section of the distiller unit, and

Figure 2 is an end elevation, also partly in section, of the unit.

In the drawing, I is a chamber having lirebrick or other walls 2.Horizontally disposed within the chamber is a plurality of closedtubular members 3 connected in series and preferably one below the otherfor gravity flow. Within each tubular member an agitator 4 of the screwconveyor type extends from the inlet end to the discharge outlet and isdriven by any suitable means 5. At the discharge end of the tube theblades of the screw conveyor are attened longitudinally to provide adischarging portion 4. The discharge outlet consists of an opening B inthe wall of the tube so arranged that the screw conveyor discharges theliquor over its lower lip 1 into a conduit 8 through which the liquorfalls directly into the inlet end of the next tube of the series withoutsubstantial contact with the wall thereof to prevent scale formationtherein. The conduit 8 discharges directly into a zone of the preliming.chamber no succeeding' .cylinder-'of the screw conveyor. Therme t ,sh

wh; iohe is used., or from .other source ;of11'.1te.1,`liui1or and lime,and iisoharees liouor irri. the "initial ,cylinder of :the uhu. .Ammoniaand water vapour 'liberated in each tubular ,member are .Withdrawnthrough pipe 11:0 and maybe ioohveyedzthroueh'smaniiold Il to the normalreugtower, ,.notfshown. 4l2 .is Ya dischargeoutlet @from ,the'last tubeof the series. The ,chamber 'i .is preferably 'hesiod vby waste heatirom-`boiler 'orgcalciner wflue gases, vbut may ,he heatedloy .directfoil, ,ses or rooal irihg es desired, and e "substantially .Constanttemperature is maintained .about Leash of the progressive ammoniadistiilihs Leibes Jin the 'unit-V '.Inoperetiohthe:usuel'pielimed'iidiior,.or liquor and lime, Vis mfed'into'thei initial 'jtube of the series andis continuously Y conveyedunder constant iagitation 'through "the shooeisisive "tubes 'to liberateprogressively' 'ammonia .unidertheinfhlenoe of the heatto whicheach'tube is subjected. The consieht eeitetionby"ih espirel :Conveyorseliminates sedimentation and ,makes :sshd :traps or the .likeunnecessary. "It also. Levoiiisssoaleiiormetionand thus .eliminates theA,heeessiiv for the :frequent cleaning -operations: reqiiire'd in y'theusual system.

ine of 'theisendtr-aesrin standard practice- The agitation .constantly'ehposeshew siiiieees .of {liouor tothe :heetedwells Lof the tubes and`Causes more rapid 'liberation "of ammonia. Since each distillation tubeis heated, rapid elimination of ammonia is effected inthe initial tubesand little ammonia is left for liberation in the nal tube of the series.This eliminates loss of ammonia in the effluent discharged through pipeI2. It will be observed that because of the location of the dischargeoutlet S and lip 1 each heated distiller tube contains a substantialbody of liquor to absorb heat from the surrounding chamber. Thus aneffective distillation temperature is maintained during the passage ofthe liquor through each tube.

The external heating of the distiller tubes avoids dilution of theliquor as when the latter is heated by injected steam in standardpractice. This gives a discharge liquor having a higher concentration ofcalcium chloride and the latter may be more economically recovered. Thetubes may be steam jacketed and thus avoid the use of the chamber l. Bythus heating the tubes the temperature of the respective tubes may bereadily varied for most eilicient liberation of the am- 3 monia. Theexternal heating of each tube at a regulated temperature permits a morerapid rate of feed of the liquor and thus increases the cap acity of thedistiller.

Hot milk of lime from the hydrator and hot liquor from the reux towermay be fed directly to the distiller, thus eliminating the usual limesettling tank and prelimer with the attendant complications. This makesuse of the heat of the milk of lime. Furthermore, the hydrator may beeliminated by feeding crushed quicklime directly into the distiller withthe hot liquor from the reux tower to utilize fully the heat ofhydration of the lime and thus reduce still further the amount ofexternal heat supply required. The continuous agitation of the screwconveyors in the distiller tubes makes this possible.

Owing to its construction the distiller unit may be operated under aninternal partial vacuum and thus further reduce the amount of heatrequired to distill the ammonia. The reduced pressure within thedistiller unit may be produced by use of the ejectors in the absorberunit as disclosed in copending application No. 540,786, now Patent No.2,446,442, issued August 3, 1948.

When yoperations are adjusted to most efcient conditions of temperatureand rate of flow, they may be maintained constant over long periodsbecause of the elimination of sedimentation, scale and the like which,in the usual system, require periodical shut-down for cleaning, and themaintenance of auxiliary equipment. In the standard system the distilleracts as a bubbling cap plate still with its constant refluxing andvarying plate concentrations. In the present system there is no reuxingin the distiller since the ammonia vapours are removed from eachdistiller tube and the concentration is effected entirely in the reuxtower. This insures easy recovery of the ammonia with reduced loss inthe effluent and, at the same time, requires a minimum of control duringcontinuous operation.

It will be observed that the distiller unit of the invention may be madeof ordinary pipe or plate and is thus much cheaper in construction thanthe standard distiller unit now in use.

The method and apparatus as specifically described with reference to therecovery of ammonia from the carbonated liquor in soda ash productionmay also be used for purifying and concentrating the waste distillerliquor. When such liquor is passed through the distiller unit lime andsodium chloride will precipitate out 4 leaving a concentrated calciumchloride brine. The precipitated solids being carried through thedistiller tubes are removed from the concentrated calcium chloridesolution.

It will also be apparent that the invention may be employed in any artwhere concentration of solutions is required and particularly in thepresence of precipitating solids. For example, in the production ofsalt, sugar and the like where continuous operation on large volumes ofsolutions is involved.

It is to be understood that various changes may be made withoutdeparting from the spirit and scope of the invention as dened in thefollowing claim.

I claim:

In the production of soda ash, the method of recovering ammonia fromfilter liquor which comprises maintaining a series of separate bodies ofpredetermined xed depth of liquor and lime, continuously feeding asupply of fresh liquor and lime to the rst body only of said series,continuously discharging a portion of the last body in the series,continuously withdrawing by gravity flow a portion of the first andintermediate bodies and feeding each withdrawn portion to the next bodyin the series, separately agitating and sweeping each body to preventsedimentation therein and to discharge solids with the liquor in eachsaid withdrawn portion, continuously subjecting all of said bodies to acommon heating medium maintained free of contact with the bodies,maintaining each of said bodies free from contact with external gases toprevent dilution therewith of the liquor and ammonia vapors arising fromsaid bodies, and separately removing said ammonia vapors from each bodyas it is liberated therefrom.

JOHN ROSS TAYLOR.

REFERENCES CITED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS Number Name Date 363,952 Frasch May 31, 1887458,798 Stroh et al Sept. 1, 1891 658,723 Naef Sept. 25, 1900 689,768Wathen Dec. 24, 1901 1,604,523 Barnhart Oct. 26, 1926 1,650,713Hennebutte Nov. 29, 1927 2,174,008 Mow Sept. 26, 1939

